Derivatives and Hedging - Schedule of amounts of derivative gains (losses) recognized in the Consolidated Financial Statements (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative [Line Items]
Gain (Loss) Currently Recognized in Accumulated Other Comprehensive Loss	$ 14	$ 6
Hedge gain (loss) to be reclassified during next twelve months	(2)
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	(4)	10
Compensation and benefits
Derivative [Line Items]
Hedge gain (loss) to be reclassified during next twelve months	0	8
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	1	13
Other General Expenses
Derivative [Line Items]
Hedge gain (loss) to be reclassified during next twelve months	4	1
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	(1)	(1)
Interest expense
Derivative [Line Items]
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	(1)	0
Other Income (Expense)
Derivative [Line Items]
Hedge gain (loss) to be reclassified during next twelve months	10	(3)
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	$ (3)	$ (2)